In thermal power generation facilities and boiler facilities, a large amount of coal and heavy oil are used as fuels. From the viewpoint of air pollution and global warming, release of carbon dioxide (hereinafter referred to as CO2) into the atmosphere has recently become a problem, and controls on CO2 emissions have been studied worldwide.
Heretofore, there has widely been known, as one of technologies of separating and recovering CO2, a chemical absorption method in which amines (for example, alkanolamine) are used as an absorbent of CO2. In case a boiler of power generation facilities is provided with a CO2 removal device in which an aqueous solution of amines (hereinafter referred to as an amine absorbent) is used, a boiler, a turbine or the like needs to undergo large-scale modification in facilities where the entire amount of a gas is discharged from the boiler. Therefore, there has been employed a so-called partial treatment in which some of an exhaust gas is diverged, introduced into a CO2 removal device and then treated, since the treatment does not require comparatively large-scale modification.
A conventional exhaust gas treatment system equipped with a device for removing CO2 by a partial treatment of such an exhaust gas includes the steps of treating an exhaust gas from a boiler by a wet desulfurization device; introducing some of the exhaust gas into a CO2 absorption column; absorbing and removing CO2 by bringing the exhaust gas into gas-liquid contact with an amine absorbent; treating the exhaust gas using an amine washing device and a demister; allowing the exhaust gas to converge with an original exhaust gas; reheating the exhaust gas so as to prevent discharge of a white smoke in a flue; and releasing the treated exhaust gas into the atmosphere from the flue. This reheating is commonly performed by heat exchange with a high-temperature exhaust gas before entering into the wet desulfurization device (Patent Literature 1).